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. There are
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W concepts
such as the NGD. The challenge is to the technology
and the people who can make it work for them. This final
part of the paper will now examine the role of imagery
within OS in meeting the needs of the future by
populating and updating the data themes that make up
existing and proposed databases.
The last 10-15 years we have witnessed some major
photogrammetric advances and successes to migrate
from the 1950's analogue technology to the analytical
instrumentation and more recently their digital equivalents
(Farrow & Murray 1992). Annually the base topographic
information database accommodates an equivalent of
900,000 units of update (these may be houses, roads,
forestry etc. - all features are measured in a common
measure of units of change). Of this number
approximately 2096 is surveyed by photogrammetric
means, by simple graphic tracing from single images to
analytical instrumentation. Superimposed vector mapping
over imagery is a very effective update mechanism.
3.2 Imagery applications in OS
The main area of recent investigation and development
has been the development of the digital mono-plotting
system based on the existing editing system. The
threshold of a production digital image system has now
been crossed and further investigations are planned.
The major reason for the adoption of a digital solution in
the past 12 months is more to do with the technological
infrastructure than with photogrammetric software
availability. Earlier OS research showed that both the
software and hardware environments were immature in
the early 1990's. The latter has progressed significantly
during the past 3-4 years with off the shelf workstations
commonplace and local area network operation speeds
increasing by a magnitude. Such is the pace of progress
that automation of basic utilities, e.g. roll film scanning
and high productivity are basic expectations that sit at the
top of the buyers' list of requirements.
3.3 The use of digital imagery in OS
Ortho-
rectification
system
Workstation/
Graphic Data
Editors - DMP
Scanner
Corporate fibre-optic network
Figure 2: The OS Digital Mono-Plotting System
103
A digital image capability has now been established in
production. Following successful trials and a production
pilot a full production system is now in operation.
The system is primarily employed on the update of rural
mapping using a single orthoimage matched centrally to
National Grid kilometre square and is referred to as DMP
(Digital Mono-Plotting system). DMP replaces some of the
graphic aerial photographic methods, successfully
employed by OS for over three decades. It will also
replace some of the current OS analogue
instrumentation.
It was a primary requirement of the development that OS
use proven techniques and software where possible since
the process involves modifying the primary asset of the
organisation, i.e. the base topographic information.
Consequently modifications were commissioned to the
existing edit system and the process is a simple
extension of the existing photogrammetric production
system.
3.4 Investigation of the potential of space imagery
OS has invested extensively in research into the potential
of space imagery over the past 15 years (Hartley 1991).
This did not produce usable results until image resolution
improved with the launch of SPOT-1 in 1986. OS then
undertook the world’s first extensive topographic mapping
project in the civilian sector. Stereo SPOT imagery was
employed to map over 25,000km? of north-east Yemen
(Murray & Farrow 1988). Other investigative work and
production projects followed. More recently this has
involved a collaboration between OS and the National
Remote Sensing Centre Ltd (NRSCL) to produce an
image map of Christmas Island (Havercroft & Fox 1993).
Benefits of space imagery: The major cost benefit of
the Yemen project was directly related to the reduction in
the number of stereo models involved. In terms of data
processing and labour it was estimated that this
contributed to an overall cost saving of approximately
10% on the (substantial) project costs (Murray 1990).
Timely data availability is a further advantage; if data can
be acquired within hours or days rather than weeks then
project planning can go ahead with confidence. Sadly the
skies over Great Britain are not always clear and
improvements in cloud penetrating techniques are always
warmly welcomed!
3.5 New Space Sensors
For space imagery to be successful in Britain we
concluded that an image resolution of 2 m or better was
required to support the applications required to maintain
the existing database. This threshold is now close to
being realised with the declassification of military
technology by the Clinton administration. There are now a
number of high spatial resolution sensors being prepared
for launch over the next few years. Table 2 provides an
overview of some of the systems proposed.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996
